In the processing of semiconductor wafers, processes such as sputter coating processes for the deposition of films, such as films of aluminum, are employed. Such processes are often carried out in machines such as, for example, that disclosed in U.S. Pat. No. 4,909,695, assigned to the assignee of the present application, and expressly incorporated by reference herein. In such machines, wafers are individually introduced from an external atmosphere, through a loadlock onto one of a plurality of wafer holders in a vertically disposed circular plate, and then moved, by rotating the plate about a horizontal axis, to index it sequentially through a plurality of processing stations in which a series of process steps are performed carried out. Such steps may include, for example, sputter etching and sputter coating steps such as those that result in application of an aluminum coating to the wafers. Typically, throughput for such a machine is slightly more than one minute per wafer for deposition of a one micron film of aluminum.
In introducing the wafers from the external atmosphere, inevitably some particulate or other contamination is introduced into the internal environment of the processing machine. Ideally, introduction of such contaminants should be totally prevented or at least kept at a minimum, as each particle or contaminant can result in a defective device on the wafer and thus reduce the ultimate value of the wafer.
Further, in such a processing machine, the performance of an initial preheating or degassing step is desirable. Such a step may be performed in the loadlock of the machine, and provision therefore has been made by a backplane heater in the apparatus disclosed in the patent incorporated above. In the loadlock chamber after being introduced from the external atmosphere, such degassing to drive off water vapor from the wafer is of limited effectiveness. Unremoved gases are a potential process contaminant that can also adversely affect the quality of a deposited film.
The processing of a wafer to produce completed semiconductor devices involves more processes than are performed in machines of the type referred to above. Some processes are performed before, and others after, introduction of the wafers into such a machine. The transporting of wafers between machines often results in contamination or deterioration of the wafers by exposure to atmosphere. With wafers coated with titanium-tungsten (TiW) films, for example, their exposure to ambient atmosphere before or after a subsequent coating cycle allows oxygen to contact and affect the TiW film, causing metallurgical change, introducing stress in the TiW film, or causing the film to fracture and flake.
In the processing of wafers described above, there is a need to increase the throughput of the wafer processing equipment, particularly equipment of the vertical carrousel type described in the patent incorporated above, and to reduce and remove contaminants from the process performed in the apparatus.
In the commonly assigned and copending U.S. patent application Ser. No. 07/701,800, entitled WAFER PROCESSING CLUSTER TOOL BATCH PREHEATING AND DEGASSING METHOD AND APPARATUS, expressly incorporated herein by reference, further needs for pre and post processing handling and treating of wafers, and for the interfacing of processing equipment with standard wafer cassette modules are set forth. In such cassette modules, wafers are horizontally oriented in a vertical stack in a plastic rack, and the modules are each sealed to a port of a transfer module and pumped to a vacuum before opening the port. The pumping of one such module typically takes more than ten minutes. Such modules may also be sealed with wafers enclosed therein and moved from machine to machine.
There is a particular need to efficiently and effectively interface wafer processing equipment, particularly of the vertical carrousel type, with such cassette modules in a way that will optimize the use of the coating machine.